1. Field of the Invention
The present invention relates to a sheet-fed printing press that includes a treatment section that includes a cylinder having a gripper for gripping each of oncoming sheets by a claw block and a claw, and a treatment means for treating the sheet in proximity to or in contact with the surface of the sheet, which is conveyed while being gripped by the gripper to the downstream side in a sheet conveying direction, and plural cylinders disposed between the treatment section and a printing impression cylinder disposed upstream or downstream of the treatment section in a sheet conveying direction, each cylinder including a gripper having the same structure as that of the aforesaid gripper.
As used herein, directional terms, “downstream” and “upstream” are used with reference to a sheet conveying direction unless otherwise specified.
2. Related Art
For example, there was already proposed a sheet-fed printing press that includes a casting device as an example of the aforesaid treatment section. This printing press has a varnishing unit disposed downstream of a printing unit in the sheet conveying direction, and a hologram forming unit disposed downstream of the varnishing unit in the sheet conveying direction. With this arrangement, a sheet of paper (hereinafter referred simply to a sheet), which is printed during passing between a blanket cylinder and an impression cylinder, of a printing unit, is transferred to an impression cylinder, which constitutes a varnishing unit, via a transfer cylinder and then varnished. Subsequently, a printed and varnished sheet is transferred to an impression cylinder, which constitutes a hologram forming unit, via a transfer cylinder, at which hologram surface is formed by pressing hologram pattern on a varnishing layer and at the same time the varnishing layer is cured by a UV radiation means, thus forming hologram (cf. Patent Document 1, for example).
(Patent Document 1) Japanese Patent Application Laid-open No. 2006-315229 (cf. FIGS. 1-3)
(Patent Document 2) Japanese Patent Application Laid-open No. Sho-63-254038 (cf FIGS. 8 and 9)
According to the disclosure of the Patent Document 1, the transferring of each sheet from the impression cylinder to the transfer cylinder and the transferring of each sheet from the transfer cylinder to the impression cylinder are carried out by the grippers of the respective cylinders, each gripper composed of a claw block and a claw. Each of these grippers, which is to convey each sheet by gripping the same along the outer circumference of the corresponding cylinder, has claws greatly projecting through the outline of the cylinder when they are kept in sheet gripping state. Therefore, when a film is pressed to the side of the impression cylinder via a printed sheet while conveying the printed sheet by gripping the same by the gripper of the impression cylinder of the hologram forming unit, the film is likely to contact the claw of the projecting gripper and hence is damaged, for which improvement is desired.
By the outline is herein meant an imaginary outer boundary of a corresponding cylinder, which corresponds to the circumference of a corresponding cylinder, and extends also through an area(s) of the circumference, where a physical circumferential surface does not exist.
Meanwhile, it is conceivable that the gripper is designed to be movable so that it is located inside of the impression cylinder during the film is pressed to the side of the impression cylinder via the printed sheet by a pressing roller. However, this arrangement is disadvantageous in the fact that it is necessary not only to design the gripper to be movable between a receiving position for receiving an oncoming printed sheet and a retracted position to which the gripper is retracted upon receiving the sheet, but also to provide an actuator for moving the gripper to the aforesaid two positions and a control unit or the like for controlling the operation of the actuator, which leads to a complicated structure. Thus, this arrangement is unlikely to he employed in practice.